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Table 1 Selection and enrollment status of Cape Cod, Massachusetts women contributing at least one index pregnancy, by initial exposure status [N (%)]

From: Prenatal drinking-water exposure to tetrachloroethylene and ischemic placental disease: a retrospective cohort study

   Initial exposure statusa
  Exposedb Unexposedc Total
Selected 1,492 1,704 3,196
Excluded during enrollment    
  Never located 132 (8.8) 136 (8.0) 268 (8.4)
  No response 245 (16.4) 336 (19.7) 581 (18.2)
  Ineligible 7 (0.5) 8 (0.5) 15 (0.5)
  Refusal 149 (10.0) 137 (8.0) 286 (8.9)
Returned questionnaire    
  Percent of located 959 (70.5) 1,087 (69.3) 2,046 (69.9)
  Percent of selected 959 (64.3) 1,087 (63.8) 2,046 (64.0)
Excluded during exposure assessment and analysis    
  Incalculable exposure—insufficient data for geocoding residential address 60 (6.3) 75 (6.9) 135 (6.6)
  Incalculable exposure-missing data on LMP 20 (2.1) 21 (1.9) 41 (2.0)
  Multiple birth 11 (1.2) 21 (1.9) 32 (1.6)
  Birth anomaly 22 (2.3) 32 (2.9) 54 (2.6)
  Missing data on key covariates 9 (0.9) 9 (0.8)d 18 (0.9)
Final sample 834 932 1,766
  1. Abbreviation: LMP last menstrual period.
  2. aThe exposure status of each pregnancy was assessed later (see Methods).
  3. bContributed ≥1 exposed index births.
  4. cContributed no exposed index births.
  5. dOne woman contributed a stillbirth only to the final analyses.